Electrical resistance and electrical heater and method of producing the same



' y 1937- B. H. N. H. HAMILTON 7 ELECTRICAL RESISTANCE AND ELECTRICALHEATER AND METHOD OF PRODUCING THE SAME Y Filed Oct. 16, 1935 3Sheets-Sheet l 3 7 2 5 r 7 w 8 h 0 a 2 s t e R e E h T s A E 10 H E M AN I E E 3 mm M AN H 5 d .I Hs

July 20, 1937 y 1937- B. H. N. H. HAMILTON 2,0$7,57Q

ELECTRICAL RESISTANCE AND ELECTRICAL HEATER AND METHOD OF PRODUCING THESAME Filed Oct. 16, 1935 3 Sheets-Sheet 3 Patented July 20,1937

ELECTRICAL RESISTANCE AND ELECTRICAE HEATER AND METHOD OF PRODUCINGBenjamin Henry Noel Hans Hamilton, London,

England, assignor to The Expanded Metal Company, Limited, London,England gAppilcatiorr October 10, 1935, sci-m No. 45,348 Y H In GreatBritain November 5, 1934 V 14.0mm. (Cl. 201-73) girder form butconsisting of simple lengths or This invention relates to electricalresistances andto electrical heaters and has for one object to provideimproved electrical resistances and heaters which may be simply andcheaply made with a minimum of waste material and which shall be compactand have great mechanical strength and high wattage dissipation per unitweight and size.

' Although not limited to its application thereto the invention is.particularly applicable to re- .sistance constructions for useinconnection with the electrical control of relatively small electricmotors and also to electrical heaters, both high temperature heaters andalso low temperature domestic and similar electrical heaters of the typesometimes termed convection heaters.

It is known tomake an electrical resistance or heater from open ormeshwork sheet metal by cutting away portions of the sheet so as tocause the current flow thrcugh'the cut away sheet to proceed in a zigzagor tortuous path. Forexample, it is known to take a sheet of metalresistance and tocut away the metal in slots which are parallel to oneanother and are transverse to the sheet there being two sets of slots,the-slots in one set extending from one side edge of the sheet but notreaching the other side edge and the slots in the other set extendingfrom the said other side edge but not reaching the first mentioned edge,the slot in one set altermating with those of the other so that thecurrent through the slotted metal is constrained to follow a zigzagpath. Known resistances and heaters constructed in this manner presentthe serious disadvantage that the slotting of the metal involves aconsiderable wastage in manufacture. while, moreover, such zigzagresistances of the simple flat sheet form are not as compact 'as isdesirable.

United States Patent No. 1,991,935 describes inter alia expanded metalresistances which do not possess the above disadvantages; for exampleFigures 12 to 14 of the said specification illustrate constructionswhich may be made very compact and involve very little wastage ofmaterial in manufacture. The resistances which form the subject ofPatent No. 1,991,935 are, however, of split tubular girder form, 1. e.in tubular form with the tube not completely closed.

The object of the. present invention is to provide resistances andheaters which shall also have the advantages of great compactness andability to be manufactured without any substantial waste of material;the'saiti'resistances and 55 heaters, however, not being of the splittubular expanded more or less flat expanded metal.

Another object is to provide an improved meth- 0d for making electricalresistances and heaters from expanded or intermedia expandedmetso-called intermediate expanded resistance or heater wherein sheetexpanded or intermediate expanded metal is cut to provide a zigzag ortortuous current path. the cuts being as nearly as possible of zerowidth (that is to say cutting away as little as possible of the metal)and the The present invention provides an expanded or metal on eitherside of each out being bent out of the general plane of the originalsheet, so

that, although the width 01. each cut is almost zero, there is amplespace in the finished resistance or heater between neighbouring lengthsof the zigzag current path, this space being obtained by virtue of thebending of the metal out of the original plane. Expanded metal per se ofcourse is wellknown, but by intermediate expanded metal is meant theslitted product obtained from slitting a sheet of metal in the wellknown slitting and stretching method of making expanded metal, but withthe stretching operation omitted.

Preferably the expanded or intermediate expanded metal when it has beencut, as above described, is bent so that adiacent lengths of the finalzigzag or tortuous path are made up of strips which are at right anglesor substantially at right-angles to the original plane of the sheet.Again preferably the cuts are at right angles to the selvedge edges. Thepreferred forms of heater or resistance in accordance-with this indiateexpanded metal (the slitt'ed product obtained from the slittingoperation in the well known slitting and stretching method of makingexpanded metal). This however, is not preferred and its application israther limited since its heat dissipating properties are obviouslyinferior to those of expanded metal.

The invention is illustrated in and further explained in connection withthe accompanying drawings. I

Figs. 1-3 show a multi-unit resistor constructed in accordance with thisinvention.

Fig. 4 shows a sheet of expanded metal before being bent. The stripsbeing half a mesh. wide.

Fig. 5 shows a side elevation ofthe resistor of Fig. 4 after beingformed.

Fig. 6 shows the zigzag current path obtained.

This is a view looking down on the resistor of Fig. 5.

Fig. 7 is a view at right angles to Fig. 5.

Figs. 8-11 correspond to Figs. 4-? except that the strips are a fullmesh wide.

Figs. 12 and 13 show different views of the clip used to mount theelement.

Fig. 14 shows the resistor fixed in place by means of the clip.

In one way of carrying out this invention a sheet S of expanded metalthe material of which will depened upon design requirements-for ex ampieit may be of any known resistance composition -is cut as shown in Figure4 with a plurality of parallel transverse cuts K1 & each of as nearly aspossible zero width. There are two sets of cuts, the alternate cuts (K1)in one sheet commencing at one side of the sheet and extending throughthe expanded metal body portion, but not extending to the other side ofthe whole sheet, while the intervening cuts (K2) in the second sheetcommence at the other side edge and do not extend to the first-mentionedside edge. The sheet of expanded metal is left with unexpanded sideedges E (which may be stamped to the shape shown) which form selvedgesand the cuts are of such length that each extends from the side in whichit commences to the selvedge at the other side without actuallyextending into the said selvedge. After the sheet has been cut as justdescribed, it is bent in such manner that the material between adjacentcuts K1 K2 lies at right angles to the original plane of the sheet, thedirection of bending alternating from end to end of the'sheet. Eachuncut portion PS of the selvedge which connects the length of materialon the front side of any one cut to the length on the rear side thereofis bent through two right angles at Q and B so that the said lengths Lof material lie at right angles to the original plane of the sheet eachlength lying immediately behind and parallel to the next. Each portionPS constitutes an unexpanded mounting portion including a centralsection included between the bending lines Q and R and two flanksections. The central sections of the severalv mounting portions liesubstantially in a common plane whereas the flank sections are bent atangles to this plane, the flank section at one end of each strip L beingbent relatively upwardly and the flank section at the opposite end ofthe strip being bent relatively downwardly. The result of the bending isto provide a succession of lengths or substantially planar strips L ofexpanded metal any two adjacent lengths being connected together at oneend by a piece of selvedge but being not connected at the other end, theconnecting piece of selvedge appearing, when viewed endwise oi. thelengths of expanded metal, as approximately of U form.

The same process of bending is continued throughout the sheet for 'anydesired length so that the final resistance product consists of a'plurality of straight flat lengths or substantially planar strips L ofexpanded metal, the lengths being parallel to and behind one another andat right angles to the original plane of the sheet. The current paththrough the whole resistance or heater, as the case may be, is a zigzagpath through all the lengths in series, the connections between adjacentlengths being constituted by the U shaped portions of selvedge. Becauseof the cutting of the slits Kr and K2 of nearly zero width as shown inFigure 4 the sum of the widths of each two strip L will be nearly equalto the distance between centers of the central sections of adjacentunexpanded mounting portions when the strips have been arranged insubstantial parallelism as shown in Figures 5, 6 and 7.

Figure 4 shows an arrangement in which the successive cuts K1 K2 arespaced apart by a distance of half a mesh of the expanded metal with theresult that the adjacent lengths L are each half a mesh acrossi that isto say each such length appears as shown in Figure 5 as a zigzagconductor. Figure 6 is a schematic view taken at right angles to Figure5 showing the way in which a zigzag current path is obtained throng. thesuccessive lengths which appear edgewise in Figure 6 (they arerepresented in this figure by broken lines) and are joined together bythe U shaped selvedge pieces which are integral therei with. Figure 7 isa view at right angles to Figure 5. Figures 8, 9, 10 and 11 are viewscorresponding to Figures 4, 5, 6 and'l respectively the diflferencebeing that in the construction shown in Figures 8, 9, 10 and 11 the cutsK1 K1 are spaced apart by a full mesh of the expanded metal and each ofthe lengths L is accordingly one mesh, instead of half a mesh, wide.

The lengths of resistance material comprised in the zigzag path may bemaintained in their desired mutual relationship by anchoring the Ushaped selvedge portions to suitable parallel carrier members which mayform part of a suit able carrier frame, the said U shaped portionstinuous or in short lengths and is threaded upon steel or other carrierIx bars CR. In this way a whole series of elements integral with oneanother niay be carried from and insulated from a pair of parallelcarrier bars, one passing through the holes A in one selvedge edge, theother passing through the holes A' in the other. Preferably the lengthsL of resistance material are mounted under slight tension .50 as toreduce liability to distortion as a result of overheating. It has beenfound that by leaving the lengths of resistance material under slighttension when cold any tendency to bowing out of the lengths of materialis avoided or at any rate reduced to unimportant minor proportions.

A multi-unit resistance in accordance with this invention is illustratedin Figures 1, 2 and 3 which show in three mutually perpendicular views afour unit construction.

Referring to Figures 1 to 3 the units are gen erally indicated by thereferences I, 2, 3 and 4 each unit consisting of a plurality of lengthsor strips L of expanded metal resistance material chorage are made tocarrier bars B which may.

be of steel and have insulation strips W laid thereon, the points ofanchorage being further insulated in any convenient manner. For example,anchorage may be made at each point by means of a nut and bolt, the boltpassing through the bar B and being insulated therefrom by a surroundinginsulating sleeve (not shown) insulating washers W beingalso provided soas to insulate the nut from the steel bar. Alternatively the points ofanchorage between the Ushaped portions and the carrier bars B may be,and preferably are made by rivets with similar provision for insulation.The bolt type of anchorage is exemplified at A13 and the rivet type atAR. Stamped interconnecters I of U form connect each unit to itsneighbour and the whole multi-unit structure is carried by end carrierrods GR in association with strip or bar members SM as clearly shown inFigure 3. It will be noted that in Figure 3 the members SM are shownbolted together at X and riveted together at Y. In practice, of course,either bolts or rivets can be used throughout, rivets being preferred.The drawings of Figure 3, however,

show both methods of construction in order to indicate that either maybe used. As will be seen these bolts or rivets, as the case may be,mechanically connect the appropriate members 'SM by clamping them withthe appropriate carrier bars B. The lead-in to the whole resistance unitis shown at LI and the lead-out at L0, and it will be apparent that all,four units are in series with one another.

When mounting and constructing the device the length Z (see Figure 2) ismade somewhat longer than the normal unstretched length 0! a portionL-between the points of anchorage and thus the said portions are putunder slight tension. 1

It will be appreciated that the cooling of a resistance or heater asshown and described will be extremely eflicient since there is greatfree- .dom for air flow. Furthermore, owing to the from the point ofview of economy of construction, residing in the fact that since thecuts expanded metal in each portion L is either one mesh (that is to sayone "diamond) or one half mesh wide, the invention is, of course, notlimited to this, and the portion L may be more than one mesh wide, ifdesired; e. g. it might be one and a half meshes wide or two meshes wideand bent back on itself as described. Again, the invention may beembodied in multi-unit constructions wherein the individual units arenot simply in series (as they are in the construction of Figures 1 to 3)for obviously parallel connection or series-parallel connection may beresorted to where-desired.

What I claim is:- e V 1. Method for making an electrical resistance orheater from a sheet of expanded metal having two oppositely disposedlongitudinal unexpanded selvedges and a body portion of expanded metaltherebetween, said method comprising cutting said expanded metal bodyportion to form a plurality of spaced substantially transverse slits ofnearly zero width, adjacent slits bounding on two sides a substantiallyplanar unit strip of ex- Again the whole conpanded metal, alternateslits extending through one and the same selvedge only and interveningslits extending through the other selvedge; then positioning said unitstrips in a plurality of planes disposed respectively at an angle to theplane of the original sheet by bending the selvedge portion to which oneend of each unit strip is connected upwardly relative to the plane ofthe original sheet, and bending the selvedge portion to which the otherend oi. the strip is connected downwardly relative to the plane of theoriginal sheet.

2. Method for making an electrical resistance or heater from a sheet ofintermediate expanded metal having two oppositely disposed longitudinalunexpanded selvedges and a body portion of expanded metal therebetween,said method comprising cutting said intermediate expanded metal bodyportion to form a plurality of spaced substantially transverse slits ornearly zero width, adjacent slits bounding on two sides a substantiallyplanar unit strip of expanded metal, alternate slits extending thoughone and the same selvedge only and intervening slits extending throughthe other selvedge; then positioning said relative to the plane of theoriginal sheet, and

bending the selvedge portion to which the other end of the strip isconnected downwardly relative to the plane of the original sheet.

'3. Method for making an electrical resistanceor heater from a sheet ofexpanded metal having two oppositely disposed longitudinal unexpandedselvedges and a body portion ofexpanded metal therebetween, said methodcomprising cutting said expanded metal body portion to form a pluralityof spaced transverse slits of nearly zero width and being disposed atright angles to said selvedges, adjacent slits bounding on two sides a.substantially planar unit strip of expanded metal, alternate slitsextending through one and the same selvedge only and intervening slitsextending through the other selvedge; then positioning said unit stripsin a plurality of planes disposed respectively at an angle to the planeof the original sheet by bending the selvedge portion to which one endof each unit strip is connected upwardly relative to the plane of theoriginal sheet, and bending the selvedge portion to which the other endof the strip is connected downwardly relative to the plane of theoriginal sheet.

4. Method for making an electrical resistance or heater from a sheet ofexpanded metal having two oppositely disposed longitudinal unexpandedselvedges and a body portion of expanded metal therebetween, said methodcomprising cutting said expanded metal body portion to form a pluralityof spaced substantially transverse slits of nearly zero width, adjacentslits bounding on two sides a substantially planar unit strip ofexpanded metal, alternate slits extending through one and the sameselvedge only and intervening slits extending through the otherselvedge; then positioning said unit strips in a plurality of planesdisposed respectively at an angle to the plane of the original sheet bybending the selvedge portion to which one end of each unit strip isconnected upwardly through ninety degrees and bending the selvedgeportion to which the other end of the strip is connected relativelydownwardly through ninety degrees.

5. In a method as deflned in claim 1, spacing the substantiallytransverse slits so as to include between adjacent slits unit strips ofexpanded metal one-half mesh wide.

6. In a method as deflned in claim 1, spacing the substantiallytransverse slits so as to include between adjacent slits unit strips orexpanded metal a plurality of half meshes wide.

7. Method for making an electrical resistance or heater from a sheet ofexpanded metal having two oppositely disposed longitudinal'unex'pandedselvedges and a body portion oi expanded metal therebetween, said methodcomprising cutting said expanded metal body portion to form a pinralityoi spaced substantially transverse slits oi nearlyv zero width, adjacentslits bounding on two sides a substantially planar unit strip ofexpanded metal, alternate slits extending through one and the sameselvedge only and intervening slits extending through the otherselvedge; then positioning said unit strips in a plurality of planesdisposed respectively at an angle to the plane of the original sheet bybending the selvedge portion to which one end of each unit strip isconnected upwardly relative to the plane of the original sheet, bendingthe selvedge portion to which the other end of the strip is connecteddownwardly relative to the plane of the original sheet; and attachingunexpanded selvedge portions to insulated supporting means with saidstrips of,

expanded metal tensioned while cold.

8. An electrical resistance element comprising a one-piece unit ofexpanded metal material, said unit including a plurality of transverselyextending substantially planar strips oi expanded metal and unexpandedmounting portions at the oppositeends of said strips, each unexpandedlying respectively in planes disposed at an angle to the planecontaining the central sections of the mounting portions, and adjacentstrips being connected togetherat one end bythe same mounting portionbut being respectively connected at their other ends to diflerentmounting portions.

9. An electrical resistance element comprising a one-piece unit ofintermediate expanded metal material, said unit including a plurality oftransversely extending substantially planar strips of intermediateexpanded metal and unexpanded mounting portions at the opposite ends ofsaid strips, each unexpanded mounting portion including a centralsection and two flank sections on opposite sides thereof, the centralsections of said mounting portions lying substantially in a commonplane, each flank section oi each mounting portion havingintegrallyconnected thereto an end of one oi said strips of intermediateexpanded metal, the flank sections at opposite ends of each stripextending respectively relatively above and below the plane containingthe central sections, said strips of expanded metal lying respectivelyin planes disposed at an angle to the plane containing the centralsections 01' the mounting portions, and adjacent strips being connectedtogether at one end by the same moun ng connected thereto an end 01' oneof said strips of expanded metal, the flank sections at opposite ends ofeach strip extendingrespectively relatively above and below the planecontaining the central sections, said strips ofexpanded metal lyingrespectively in planes disposed at an angle to the plane containing thecentral sections of the mounting portions, and adjacent strips beingconnected together at one end by the same mounting portion but beingrespectively connected at their other ends to different mountingportions, the sum of the widths of each two strips of expanded metalbeing nearly equal to the distance between centers of the centralsections of adjacent unexpanded mounting portions when said strips arearranged in substantial parallelism. i i

11. An electrical resistance element compris ing a one-piece unit ofexpanded metal material,

said unit including a plurality of transversely extending substantiallyplanar strips oi expanded metal and unexpanded mounting portions at theopposite ends of said strips, each unexpanded mounting portion includinga central section and two flank sections on opposite sides thereof thecentral sections of said mounting portions lying substantially in acommon plane, each flank section of each mounting portion havingintegrally connected thereto an end 0! one of said strips of expandedmetal, the flank sections at opposite ends of each strip extendingrespectively relatively above and belowand at right angles to the planecontaining the central sections, said strips of expanded metal lyingrespectively in planes disposed at an angle to the plane containing thecentral sections of the mounting portions, and adjacent strips beingconnected together at one end by the same mounting portion but beingrespectively connected at their other ends to diil'erent mountingportions.

12. An electrical resistance element as defined in claim 8 in which thesubstantially planar strips of expanded metal are one-half mesh wide.

13. An electrical resistance element as defined in claim 8 in which thesubstantially planar strips I of expanded metal are a plurality of halfmeshes wide.

14. An electrical resistance element comprising a one-piece unit ofexpanded metal material, said unit including a plurality of transverselyextending substantially planar strips 01' expanded metal and unexpandedmounting portions at the opposite ends 01 said strips, each unexpandedmounting portion including a central section and two flank sections onopposite sides thereof, the central sections of said mounting portionslying substantially in a common plane, each flank section 01 eachmounting portion having integrally connected thereto an end of one ofsaid strips of expanded metal, the flank sections at opposite ends 01each strip extending respectively relatively above and below the planecontaining the central sections, said strips of expanded metal lyingrespectively in planes disposed at an angle to the plane containing thecentral sections of the mounting portions, and adjacent strips beingconnected together at one end by the same mounting portion but beingrespectively connected at their other ends to different mountingp'ortions; and an insulated support connected to said unexpandedmounting portions and mounting said strips of expanded metal undertension when cold.

BENJAMIN HENRY NOEL HANS HAMILTON.

